The History of Electric Flight
Part I: Pioneers Colonel H. J. Taplin and Fred Militky
Prologue
Electric power is increasingly important to the model soaring world these days, from the front end sustainers and ‘up-and-go’ systems on scale gliders to the proliferation of competition classes for electric powered gliders and also to the RTF foamies that we see every weekend at our local flying field. A couple of years ago I wrote a series of articles about the history of electric flight for my regular Radio Days column in SAM Speaks, the monthly magazine of SAM35 in the UK. These days the UK Chapter of the Society of Antique Modellers is not just about old timer and vintage models but embraces all of traditional aeromodelling and electric power is often substituted for the noisy and smelly sparkies and glow motors of the past — we still love British diesels and Japanese four strokes though!
I mentioned the electric flight series to Terence and he suggested that I contribute a version of it to New RC Soaring Digest and here is the first part of that. Before we start I have a couple of caveats. Firstly, this is a personal view of the history of electric flight. It is not scholarly or definitive and it would be very interesting to hear other views on how the technology developed. Secondly, it is not just about gliders and sailplanes although they are a very important part of the story. So with background and caveats out of the way, let’s begin:
Colonel H. J. Taplin
Apart from a few unsubstantiated reports of electric powered free flight models from the early 20th century and some control line experiments with power fed down the lines, the first documented electric model aircraft flight was with an RC model on June 30th, 1957. The model was designed and built by Colonel H. J. Taplin of Taplin Twin (twin cylinder classic British diesel engine) fame. The story of the model and its first flight at Chalgrove airfield in Oxfordshire is well documented in the September 1957 Aeromodeller magazine. Incidentally, Chalgrove airfield is still active and currently home to the Martin-Baker Company who design and make most of the western world’s ejection seats.
The Colonel used a 24V American electric motor from the Emerson Company. Emerson are still in business making a wide variety of electric and electronic products which, unfortunately, do not include motors for RC models! The electricity was provided by a bank of Venner silver zinc cells with a nominal voltage of 1.2V per cell. The 20 cells used initially did not provide enough power for flight so a further five were added to give a nominal 30V at 8A which was, reportedly, enough to take off from a smooth surface. The model weighed 8lb so would have been marginally powered by 240W — a bit less than a third of a horsepower — input to the motor or 30W/lb, particularly as the motor was being overdriven so would not have been very efficient. Nevertheless this was a magnificent achievement for the time and a tribute to the vision and engineering skills of the Colonel.
The Aeromodeller demonstration was not a one off. There is an interesting British Pathé Pictorial colour film showing Taplin demonstrating the electric model aircraft and an RC boat powered by a 10cc four stroke engine. I have included some screen shots from the film which is in colour and is a fascinating record of a pioneering project.Unfortunately there is only a brief glimpse of the model in flight but it does seem to be climbing away well from a hand launch by the Colonel and is under the control of (presumably) Taplin junior. You can find the link to the entire film in Resources, below.
The model used by the Colonel was a variant of his Radio Queen design that dated back to 1950. There is a plan of the model on Outerzone and can find the link in Resources, also. The design became famous in 1954 when it was used for the first UK Channel crossing by an RC model. The channel-crossing version was powered by an ED diesel engine and controlled by ED three channel reed radio. The British Daily Express newspaper provided sponsorship and publicity, something that is unlikely to happen these days!
Fred Militky
The next key chapter of the history moves to Germany and revolves around the famous Graupner model company’s chief designer and a not-so-famous inventor of electric motor technology.
Throughout his time as editor of Aeromodeller, Ron Moulton was always keen, through his network of international contacts, to bring the cutting edge of aeromodelling technology to the readers of that esteemed journal. The bumper December issues of the magazine were always eagerly awaited and the December 1959 issue was no exception, not least because it included the story of (presumably, as there is no author credited) Ron’s trip to the Graupner factory in Germany to witness pioneering electric flight in action.
Ron reported that Fred Militky, Graupner’s design and development engineer, had been researching electric free flight since 1941 but had only begun to have success around 1957 with a ‘special motor’ presumably hand built by himself. The advent of a new commercially built motor in 1959 had transformed the performance of Militky’s models, however, and Ron witnessed a 22 minute out-of-sight flight of Militky’s Elektroflug 251 model from a three minute motor run. Ron didn’t report if the model was ever found! E 251 was Militky’s 251st model so he was clearly a prolific designer and builder. After Ron’s return to the UK, a flight of 23 minutes, witnessed from a Jodel lightplane, was recorded from a one-to-two minute motor run in Elektroflug 248, an earlier version of the model.
The motor that made all the difference was the invention of Dr Ing. Fritz Faulhaber who walked in to the offices of the German Modell magazine in February 1959 to see if his new invention could be of use to the modelling world as a servo motor. The Micromax motor was of coreless design with a self-supporting armature winding rotating around a static magnet. This avoided the ‘cogging’ of typical DC motors and gave both high efficiency and the ability to run on low voltages. The same type of motor construction is used in high quality RC servos today. Faulhaber went one step further by integrating the motor with a miniature gearbox which was available in a number of different ratios. The geared motor only weighed 0.9oz! Militky’s experiments showed that the 15:1 ratio was ideal for free flight on 4–6V driving a prop between 10 and 14 inches. The story of the motor was described in detail in an article in Aeromodeller in March 1960.
The Micromax motor was also used in the servos for the Graupner Bellaphon RC system. The large advertising model for the radio can be seen on top of the Graupner company bus in one of the photos of Militky with his pioneering FM 248 model. The Faulhaber company is still very much in business these days and still produces high precision DC motors based on the original Faulhaber design.
The other key issue, as always for electric flight, was battery power. Again technology developed outside the modelling world was adapted in the form of miniature sealed lead acid cells originally developed for cigarette lighters and intended for a single use without recharging. These were known as Rulag batteries in Germany and Magnatex in the UK. A 350mAh version weighing 0.875oz was the one chosen by Militky and a pair of these in series this gave 4V and enough power for a dozen or so flights. Militky found that the cells could be recharged but there was no fast charging in those days, however. The recommended charge was at 15mA overnight and, if overdone, the cell casing would blow up like a balloon! It was also possible to use three ‘high performance’, non-rechargeable (early alkaline?) pencells at 4.5V but with lower performance.
The March 1960 Aeromodeller article also described the Aeromodeller staff experiments with the new motor and the lead acid cells. After an initial failure with a polystyrene delta which flew too fast for the propulsion system they modified an Aeromodeller Plans Service Rubberdub rubber model which was about the same weight and size as the German models. This was immediately successful and showed that good performance could be obtained by the average aeromodeller.
The 1960–61 Aeromodeller Annual had an article repeating much of the two magazine articles but also introducing the first commercial electric flight model in kit form, the Graupner Silentius.
This was clearly a refined and productionised version of Militky’s experimental models and, in typical Graupner fashion, was highly engineered with excellent plans and instructions. The catalogue stated that the kit was for experienced modellers, however, the box art now sported a canopy and pilot!
The plan included a very nice isometric view that I have included here to show how it all fitted together. The plan and supporting articles are available on Outerzone and linked in Resources.
The model was reviewed by the famous USA modeller Bill Winter in the American Popular Science magazine in March 1961. Interestingly he compared it with a Japanese model that was available in the USA at the time that used a very simple conventional geared motor. Winter was impressed by Silentius and its motor but concerned that it was expensive at around $15 complete. He said that by comparison the Japanese motor:
“the AP 35, has a gear reduction of about 7:1 and spins a shorter 9–1/2 in prop a little faster, at about 1,500 rpm. It’s somewhat less powerful than the German motor, but it has sturdy bronze bearings and modem ceramic magnets. The model, known as the TK-1, is bigger, with a 38 in wingspan, but has a more primitive stick-like fuselage reminiscent of early rubber-band models. This, however, makes it considerably cheaper — less than $6 including motor — and also simplifies assembly. It weighs about 6–3/4 ounces ready to fly. The parts in the … kit are already cut out for you; those in the German kit aren’t. Both kits come with complete instructions in English.”
The Japanese model used four pencells for power and was clearly much less refined than Silentius. It did, however, have a neat freewheel device on the motor. Unfortunately Winter did not report on the performance of the Japanese model so it is not clear how practical it was. I do not remember the TK-1 being available in the UK at the time. It would be interesting to hear if anyone had any experiences with one.
Fred Militky continued to pioneer electric flight and his work was recalled in a presentation at the AVT-209 workshop in Lisbon, Portugal in 2012 by Dr. Martin Hepperle of the DLR Institute of Aerodynamics and Flow Technology in Braunschweig, Germany (and famous for his MH series aerofoils, see link below in Resources). Hepperle discussed the seminal work by Militky, who as chief engineer at Graupner, a model aircraft firm, went from designing small electric models to the MB-E1, the world’s first person-carrying electric aircraft. Hepperle wrote:
“[t]here is nothing new under the sun … One of the Pioneers of Electric Flight, Fred Militky began with 1940 first trials, and after 1945 became chief engineer at Graupner”
His electric motor glider MB-E1 — a Brditschka HB-3 with a span of 12m and a weight of 440kg — flew on October 21, 1973. The flight lasted about 11 minutes and reached an altitude of 360m piloted by Heino Brditschka. Its Bosch 13hp motor was driven by Varta nickel-cadmium batteries. The two-seater had become a one-seater with a large energy storage compartment behind the pilot. There is a video of this flight which you can find linked in Resources, below.
Next time, more about Fred Militky and the RC electric gliders he designed for Graupner. As I mentioned above in the Prologue, I would be very interesting to hear other views on how the technology developed — please leave those thoughts in the Responses section below, which you can access by clicking the 💬.
Thank you so much for reading and see you next time!
©2023 Mike Goulette
Resources
- Electrically Powered Model Planes from British Pathé Ltd. — “This is Colonel H. J. Taplin, a man who builds these radio controlled electrically powered models…”
- Radio Queen plans from Outerzone. — “Famously the first RC model to fly across the English Channnel in September 1954. … Both old and modern construction is shown on the plan…”
- Silentius plans from Outerzone. — “Free flight sport model, for electric power. Wingspan 780 mm. Wing area 140 sq in … Silentius was … the world’s first kit for an electric-powered free flight model airplane…”
- MH Airfoils from Martin Hepperle. — “This is a web site about model aircraft, airfoils, propellers and aerodynamics…”
- World’s First Electric Flight 21st October 1973 on YouTube. — “First manned electric powered flight in Wels, Austria on 21st October 1973…”
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